THE GREAT ERUPTION OF SAKURA-JIMA IN 1914. 175 



The rock at the water's edge is weakly vitreous, dark- 

 gi'ay, somewhat slaggy and dopatie. As usual, the phenocrysts of 

 andesine-plagioclase are abundant, whik^ those of pyroxenes com- 

 paratively few, of which the prismatic hypersthene slightly pre- 

 dominates over anhedral augite. The hyalopilitic groundmass 

 (PI. XVIII. Fig. 7) is built up of dusted augite needles, mixed with 

 a slightly smaller quantity of feldspar laths in a light-brownish glass. 

 Microscopic flecks are seen, being caused, as usual in subaqueous 

 lavas, by globulitization and decolorization of the base. The lighter 

 shade of rock is caused by the minuteness of size but not the 

 quantity of augite microlites in the groundmass. 



The lava on the slope is of a grayish black type with 

 slaggy sempatic fabric. The phenocrysts are likewise plagioclase 

 and pyroxenes, the latter being comparatively abundant as com- 

 pared with the other historic lavas. The dominant pyroxene is 

 hypersthene. Anhedral olivine again occurs sporadically. The 

 glass base is colorless, but if the brown glass partakes of the 

 groundmass in appreciable amount, the rock becomes vitreous and 

 black. 



ß) The lavas of the Kômen area (the N.E. coast) are also 

 divisible into those on land and shore. The former contains a 

 comparatively large amount of hypersthene. The groundmass 

 (PI. XVIII. Fig. 8) is full of augite microlites, intermixed with a 

 little larger feldspar iu the chocolate-brown glass. The latter is 

 characterized by minute texture (PL XIX. Fig. 1), of which there 

 are two types, one variety Ijeing dark with a brown glassy base 

 and augite microlite, the other being gray owing to very fine 

 augite needles in the colorless glass. The common feature is the 

 oc<;asional appearance of anhedral olivine and the decided pre- 

 dominance of hypersthene over augite among phenocrysts. 



